The measurement of temperature in medical treatments and therapies, in particular also in surgery, is of importance in many ways, in particular for determining a progress in the therapy or treatment, to control it and, as the case may be, finish it.
With conventional temperature sensors, an uninfluenced measurement of temperature parallel to ongoing therapies or treatment measures, in particular also surgical interventions, is not possible in many cases, as there is a multitude of environmental factors which affect the measurement of temperature and thus falsify the temperature value actually to be determined.
To give an example, both electric disturbances in surgical RF devices and the direct warming up of the sensors when heated by a laser beam play an important role as disturbing factors. In electrosurgical interventions, a control of the process is accomplished at present by measuring the electric impedance of the treated tissue structure, correlating with the water content of the tissue structure. During the supply of RF current, however, the measurement of temperature cannot be performed.
Also in the case of applying lasers, a direct measurement of temperature by means of thermocouples or thermistors is not possible due to the inherent absorption of laser energy by these elements.
The above-mentioned measurement of the impedance is capable of reflecting the reaction of the tissue structure to the thermal stimulus only as an indirect quantity. A substantial change in the impedance, however, only occurs if a considerable amount of the tissue water is evaporated. Indeed, the tissue structure itself is affected and altered already at significantly lower temperatures. By way of example, conformation modifications in the collagen are already reached at temperatures of approximately 70° C. Apart from the temperature, also the exposure time of the temperature stimulus plays an important role. Such processes as well as other chemical reactions are described by the Arrhenius coefficient.
Further, the measurement of impedance is highly dependent on the size of the area of the tissue structure relevant in the measuring process as well as on the distance and contact pressure of the electrodes.
Furthermore, document WO 2009/005850 A1 discloses to use the measurement of the light transmission for evaluating the state of the treated tissue. This measurement process is prone to malfunctions with respect to soiling and in many cases is not sufficiently meaningful regarding the state reached by the observed tissue.